2/2 FtANT GROWTH SUESTANXES 



ad^'nine «Tk3 l.VA or NAA W»c! to madced enlarjfemeru and cell division 



in rhe tiicajcs of the <i«Tn se^rmcnts paitioulariy of ihe pith and superficial 

 oortioal layers. How^exer, :he relative grox^th of the different tissues 



deycixls on the relatix-e concentrations of the two substances. 



"Dje evtent of or^jan formation i? also dependent on both the concen- 

 trations aj>d proportions of adenine and auxin. For example in the 

 treatments i^jo^'n in Ficfure 2. with high adenine and relatively low I.\.\, 

 tiftere is x'er\- rapid {growth of the oripnal tissues and of new parenchyma, 

 bat t^crc is no organ formation, \\ith higher concentrations of I.\.\, 

 loot fonnation occurs even though it is much less than would be obtained 

 fiom dte same ooncentrations of lAA in the absence of adoiine. The 

 resahs obtaaned %ith high adenine and only minute concentrations of 

 l.V\ are iUustratcd in Figure 5. Here the formation of buds is restricted 

 to the acropetal ends of the segments and roots usually form later at the 

 bases of the buds and/or at the basipetal ends of the stem segments. 



In generaL therefore the results indicate that under the conditions of 

 these experiments the tx'pes of growth and organ formation u-hich occur 

 are determined b^- the concentrations of auxin and adenine supplied in 

 die nutrienr medium. Relatively high auxin concentrations £avor tlic 

 fo rma riran of roots and prex'ent the formatitwi of buds. High adenine 

 concentrations fax'or the formation of buds and decrease the extent of 

 root formation. With both substances added together in proper con- 

 centrations it is possible to get marked stimulation of growth widiout 

 organ formation. 



Corr^arathf experiments wjih horse radish and carrot root segments. — ^The 

 results obtained with tobacco stem segments indicate tliiat the morpho- 

 genctic response to treatments ■with adenine and L\-\ must var\^ with the 

 tissue conyosition- Hence considerable variabilir\' in responses is to be 

 expected between different organs of the same plant and particularly 

 between different species. Tests "were, therefore, carried out with horse 

 radish and zi — ■ — "" which can be conveniently^ culturedL The 

 former mateLr..i_ ^-^t ^1. because it has a marked capacity to fonn 



--'•—"'"-,■• ''■ :\^ and : ;_: reason has been used cxtcosivciy in work 

 (7j. A - ^7 re 6, omtnJ segqieats of hocse 



^"-odoced oa the average ooe 



. rie the number of bods was 



- : TTie xwesence of L\.\ e\'en 

 . ^ . . _. __. - : ; tnted the fotmatioo of 



